Jester David
Hero
Because there's so much else they could do.I don't see why it is unlikely to see these two new classes released in Fall 18...?
With one book each year, devoting two books in a row to classes & subclasses is a lot. And it really delays every other book. It'd be like doing another monster book this fall.
I'm expecting a book on magic items, artifacts, and the like next year. But it could be high level monsters & epic content, something related to the planes, a hacker's guide, or other ideas.